(IJCSIS) International Journal of Computer Science and Information Security, Vol. 3, No. 1, 2009

Transmission Performance Analysis of Digital Wire and Optical Links in Local and Wide Areas Optical Networks

Abd El–Naser A. Mohamed1, Mohamed M. E. El-Halawany2 Ahmed Nabih Zaki Rashed3* , and Amina E. M. El-Nabawy4 1,2,3,4Electronics and Electrical Communication Engineering Department Faculty of Electronic Engineering, Menouf 32951, Menoufia University, EGYPT 1E-mail: [email protected], 3*E-mail: [email protected]

Tel.: +2 048-3660-617, : +2 048-3660-617

Abstract—In the present paper, the transmission detector even as the transceivers’ pointing drift. This scheme performance analysis of digital wire and wireless optical is acceptable for low data rates, but becomes increasingly links in local and wide areas optical networks have been challenging at multi-Gb/s rates. Our approach has been to modeled and parametrically investigated over wide range shift the burden from the communication system to a of the affecting parameters. Moreover, we have analyzed tracking system that keeps the pointing jitter/drift to less the basic equations of the comparative study of the than 100 μrad. With such small residual jitter, sub- performance of digital fiber optic links with wire and milliradian transmitted beam widths can be used. In so wireless optical links. The development of optical doing, the part of the system is wireless communication systems is accelerating as a high relatively simple and allows us to scale up to, and even cost effective to wire fiber optic links. The optical beyond, 10 Gb/s. The main challenge for optical wireless is wireless technology is used mostly in wide atmospheric attenuation. Attenuation as high as 300 dB/km data transmission applications. Finally, we have in very heavy fog is occasionally observed in some locations investigated the maximum transmission distance and around the world [3]. It is impossible to imagine a data transmission bit rates that can be achieved within communication system that would tolerate hundreds of dB digital wire and wireless optical links for local and wide attenuation. Thus, either link distance and/or link availability areas optical network applications. has to be compromised. It is also obvious, that the more link margin could be allotted to the atmospheric attenuation, the Keywords—Wireless fiber optics; Transmission distance; better the compromise is. As a result, in the presence of Transmission bit rate; Radio frequency; Bit error rate; severe atmospheric attenuation, an optical link with narrow Digital optical links; ; Wide area beam and tracking has an advantage over a link without Network. tracking [4]. Recent years have seen a wide spread adoption of optical technologies [5] in the core and metropolitan area networks. Wavelength Division (WDM) transmission systems can currently support Tb/s capacities. I. INTRODUCTION AND BACKGROUND Next generation Fiber-to-the-Home (FTTH) access networks are expected to rely on Passive Optical Networks (PONs) in Optical Wireless communication, also known as free- order to deliver reliable, multi-megabit rates to the buildings space optical (FSO), has emerged as a commercially viable serviced by the network. Time Division Multiplexing PON alternative to RF and millimeter-wave wireless for reliable (TDM/PON) and Wavelength Division Multiplexing PON and rapid deployment of data and voice networks [1]. RF (WDM/PON) may constitute a reliable alternative to the and millimeter-wave technologies allow rapid deployment of Active PON, where routing is done using a large wireless networks with data rates from tens of Mb/s (point- switch. However, as optical technologies are starting to to-multipoint) up to several hundred Mb/s (point-to-point). migrate towards the access networks the cost factor is a vital However, spectrum licensing issues and interference at issue [6] to the economic prospects of the investments. unlicensed bands will limit their market penetration [2]. Unless significant progress is achieved in optical component Though emerging license-free bands appear promising, they integration in the near future, in terms of the scale of still have certain bandwidth and range limitations. Optical integration and functionality, the cost of the optoelectronic wireless can augment RF and millimeter-wave links with components is not expected to diminish in view of the light very high (>1 Gb/s) bandwidth. In fact, it is widely believed specifications placed by TDM/PON and WDM/PON. More that optical wireless is best suited for multi-Gb/s importantly, if the existing duct availability is limited, one communication. The biggest advantage of optical wireless may expect large investment costs due to the enormous fiber communication is that an extremely narrow beam can be roll out required. Free-Space Optics (FSO) is being used. As a result, space loss could be virtually eliminated considered as an attractive candidate in order to establish (<10 dB). But few vendors take advantage of this and use a ultra high Gb/s wireless connections. FSO systems are wide beam to ensure enough signal is received on the classified as indoor (optical LANs) and outdoor systems. (IJCSIS) International Journal of Computer Science and Information Security, Vol. 3, No. 1, 2009

FSO is sometimes referred to as optical wireless since it therefore designed to have a power margin. Another basically consists of transmitting the optical signal directly important issue is the misalignment caused by building into the atmosphere without the use of an . FSO sways [7] due to thermal expansion, wind sway and systems have high bit rates (1Gb/s is already commercially vibration. Using systems with larger beam divergence available, while 10 Gb/s systems may soon appear). WDM however may mitigate some of these effects. Automatic technology may also provide a further increase in the tracking techniques have been developed to deal with this aggregate transmission capacity exceeding 100 Gb/s. problem. However, as light is no longer guided by the optical fiber, In the present study, we have investigated the the performance of outdoor FSO systems is mainly limited transmission performance analysis of digital wire and by environmental factors. It is widely recognized that fog is wireless optical links in local and wide areas optical network the worst weather condition for FSO systems causing over wide range of the affecting parameters. Moreover, we attenuation that might well exceed 100 dB/Km under heavy have analyzed parametrically and numerically the maximum fog conditions. Atmospheric scintillation, i.e. the change of transmission distance and transmission bit rates that can be light intensity in time is also another limiting factor. The achieved within digital wire and wireless optical links for scintillations, caused by random, thermally induced optical networks. fluctuations of the refractive index along the propagation path, result in bit error rate penalties and FSO systems are

II. SIMPLIFIED OPTICAL NETWORK ARCHITECTURE WITH WIRE AND WIRELESS OPTICAL LINKS

Optical Supported detector ONU1 number of Information Optical users Source Source

. Wireless x

x . u . . u optical link

M .

DM .

Information Optical Source Source Wire Optical fiber link Supported

Optical ONUn number of detector users OLT

RN

Figure 1. Simplified optical network Architecture Model with wire and wireless optical links.

The architecture model of passive optical network with multiplexed by Mux. When traffic arrives at RN, different optical links is shown in Fig. 1. PON consists of wavelengths are demultiplexed by Demux and sent to optical many laser diodes as a source of optical signals which detector [Avalanch or PIN photodiode] convert converts the electrical signal in the information source to the optical signal into electrical signal and then sent to optical signal, multiplexer (Mux) in the OLT, different ONUs which is distributed to different number of supported optical fiber links, demultiplexer (Demux), optical network users. Wavelength division multiplexing passive optical unit (ONU) in the remote (RN), optical detector which networks has been regarded as a promising technology to converts the optical signal to electrical signal for processing meet the demands of various customers or most supported to ONU and connects to the supported number of users. In subscribers which include many kinds of broadband data the transmission direction, the information source (electrical such as a high speed , high data transmission data signal) is transmitted from the backbone network to the OLT rate wireless transmission, and a real time video service. and according to different users and location, optical source Recently, various techniques of access networks have been [laser diode or light emitting diode] convert it in to optical presented to increase transmission capacity, transmission signal and is transmitted into corresponding wavelength and distance and reduce the cost per supported user. (IJCSIS) International Journal of Computer Science and Information Security, Vol. 3, No. 1, 2009

II. 1. Simplified basic configuration of digital wireless system

Data in Modulator Driver Laser Telescope

Channel (Atmosphere)

Data out Electro-optic Amplifier Optical filter Telescope Detector

Figure 2. Basic configuration of wireless optical communication system.

s

Data LD s PD Data n n

e e l l

Figure 3. Schematic view of the configuration of wireless optical link.

Figures (2, 3) show the basic configuration of wireless wavelength. The short wavelength in the range of 0.78-0.8 optical communication system link. The link consists of an µm was first introduced to transmit a lower data rate. The electrical/optical (E/O) conversion device and an long wavelength which is used for the fiber optic systems is optical/electrical conversion (O/E) device. The E/O in the range of 1.3-1.5 µm [8]. The advantage of the long conversion is accomplished by either the laser diode or the wavelength is that the optical amplifiers are now available, external modulator, while the O/E conversion by the and because of the amplification of optical carrier the photodiode such as PIN diode and APD. The transmission transmission distance between a hub station and a subscriber data rate is dependent on the modulation speed of the E/O terminal can be increased. The output power of the link devices. The wavelength division multiplexed (WDM) should be designed by taken into account of the eye safety. technology can increase the transmission capacity using a Optical fiber maintenance is a very important issue to be number of laser diodes and with multiplexers. consider in developing a high quality and reliable passive The wireless optical link is used for point-to-point optical network [9]. applications such as the access link between a hub station and a subscriber terminal. The important parameter for the wireless optical communication link is an optical

II. 2. Simplified basic configuration of digital wire optical cable link

Optical signal Data out

Data in Optical Optical fiber channel Optical Supported number of users transmitter detector

Figure 4. Basic configuration of digital optical link. (IJCSIS) International Journal of Computer Science and Information Security, Vol. 3, No. 1, 2009

As shown in Fig. 4, the basic architecture view of the 57.295 A P = P . receiver e−αL (1) configuration of the digital optical link. Digital received transmit 2 ()θ L communications systems have many advantages over analogue systems brought about by the need to detect only where preceived is the power at receiver (watt), Ptransmit is the transmission power (watt), Areceiver is the receiver effective the presence or absence of a pulse rather than measure the 2 absolute pulse shape. Such a decision can be made with area (m ), θ is the beam divergence (degrees), L is the length reasonable accuracy even if the pulses are distorted and of the optical link (m), and α is the atmosphere absorption noisy. For single wavelength systems, repeaters allow new (dB/Km). The total loss coefficient is determined by: clean pulses to be generated if required, preventing the σ L = σ rain L + σ fog L + σ snow L + σ sc int illation (2) accumulation of distortion and noise along the path. In -1 where σrain is the absorption due to rain (Km ), σfog is the optical communications systems, the pulse sequence is -1 absorption due to fog (Km ), σsnow is the absorption due to formed by turning on and off an optical source either directly -1 snow (Km ), and σscin is the absorption due to scintillation or using an external modulator. The presence of a light pulse -1 (Km ). A variety of models exist for the calculation of these would correspond to a binary 1 and the absence to a binary absorption coefficients. In the case of fog, the Kruse model 0. The two commonly used techniques for representing the according to: digital pulse train are non return to zero (NRZ) and return to −q zero (RZ). In the case of NRZ, the duration of each pulse is 3.912 ⎛ λ ⎞ σ (Km−1) = ⎜ ⎟ (3) equal to twice the duration of the equivalent RZ pulse. The fog ⎜ ⎟ V ⎝ λ0 ⎠ choice of scheme depends on several factors such as synchronisation, drift etc. An ac coupled photoreceiver will where V is the visibility at (λ=λ0), Km, λ is the actual generally not pass a signal with long sequences of ’1’s or wavelength of the beam, µm, λ0 is the reference wavelength ’0’s and so some form of RZ coding scheme would be in µm for the calculation of V, and the exponent q is the size distribution of the scattering particles and is equal to 1.3 if 6 required [10]. 1/3 Km < V < 50 Km, and equal to 0.585 V for low visibility V < 6 Km. Also to calculate the optical losses due to snow, the III. BASIC SYSTEM MODEL AND empiricial formula can be used: b EQUATIONS ANALYSIS σ snow (dB / Km) = A S (4) There are several important system issues that need to be where S is the snow fall rate (in mm/hour), A=5.42x10-5 λ+ considered in the theoretical model equations analysis of 5.9458, and b= 1.38. In the same way, to calculate the such an arrangement of digital wire or wireless optical cable optical losses due to rain, the empiricial formula can be links: used: i) Optical signal wavelength: Most installed fibre is σ (dB / Km) =1.076 R2 3 (5) designed for use at 1.3 µm. If long haul links are rain necessary and multiple wavelength channels are needed where R is the rain fall rate measure (in mm/hour). Finally then the wavelength must be in the 1.55 µm region. the optical loss due to scitillation is calculated using the Single channel links can be implemented with a 1.3 µm following expression [11]: system using optical repeaters to extend the reach. ⎛ 7 6 ⎞ 2 ⎜ ⎛ 2π 9 ⎞ ⎟ 2 11 6 ii) Digital wireless: wireless modulation avoids the σ sc = 4. 23.17⎜ 10 ⎟ Cn L (6) ⎜ λ ⎟ requirement for samplers and digitisers at each telescope ⎝ ⎝ ⎠ ⎠ site allowing these to be situated at the correlator. 2 -2/3 where Cn is the scintillation strength (in m ). It should be Digital systems are much less prone to noise and non- noted that the case of wireless optical link system, fog linear effects and so can offer better quality signals over induced absorption is the most impairment and can be larger distances. significantly affect the performance of the system. A link iii) Length of link: This will have an impact on the budget for wireless optical link using one lens in the modulation technique used and the need for mid-span transmitter and one lens in the receiver is calculated. optical amplifiers (or electrical repeaters for single Different kind of losses are calculated that may cause power wavelength channels). losses during transmission [11]. The factors that cause the iv) Data rate: If a digital implementation is chosen, the majority of the losses for the system are the atmosphere data rate will define the maximum instantaneous attenuation and ray losses. bandwidth and hence the sensitivity of the radio Equation (7) shows that the ray losses of the system depend astronomy measurement. Commercial equipment will on the radius of the receiver lens and the beam radius at the require standard data rates to be used (2.5Gbps, receiver unit. A Gussian beam intensity distribution is 10Gbps) which may not be compatible with the radio assumed [12]: astronomy front and back end. ⎛ 2 R 2 ⎞ ⎜ − ⎟ Preceiver w ()L III. 1. Wireless optical link design Fs = 10log = 10log⎜1 − e ⎟ (7) In the design of wireless optical link system, it is Ptotal ⎜ ⎟ important to determine the link budget equation. The general ⎝ ⎠ link budget equation is given by [11]: (IJCSIS) International Journal of Computer Science and Information Security, Vol. 3, No. 1, 2009

where L is the link distance, Km, FS is the ray losses, dB, wavelengths. As it traverses the fibre, the shorter wavelength Ptotal is the total beam power at L, watt, R is the lens radius components travel faster than the longer wavelength ,mm, w (L) is the beam radius, mm. Geometrical losses components and as a result, each pulse experiences occur due to the diverence of the optical beam. These losses broadening. By the time the pulses reach the receiver, they can be calculated using the following formula [12]: may have broadened over several bit periods and be a source 2 of errors (inter symbol interference). The measure of A ⎛ 57.295 D ⎞ R ⎜ R ⎟ chromatic dispersion is D, in units of psec/nm.km, which is = ⎜ ⎟ , (8) AT ⎝ DT + 100. d.θ ⎠ the amount of broadening in picoseconds that would occur in where AR is the effective area of the receiver lens, AT is the a pulse with a bandwidth of 1nm while propagating through effective area of the transmitter lens, DR is the diameter of 1km of fibre. The chromatic dispersion factor is given by the transmitting lens, DT is the diameter of the receiving [13]: lens, d is the distance between the wireless optical λ γ = B2 L D , (15) transmitter and receiver, θ is the divergence of the π c transmitted laser beam in degrees. Based on curve fitting where B is the data rate, L is the fiber path length, and c is Matlab Program, the fitting equations between optical signal the speed of light in a vacuum. As the optical components to noise ratio (OSNR), the operting signal wavelength for propagate through the fibre, the inherent birefringence transmitter and receiver, and the wireless optical link length causes one of the components to be delayed with respect to are [13]: the other. In high bit rate systems, this differential group 2 3 OSNR = 17.35 − 12.27 L + 7.05 L − 5.87 L , (9) delay can lead to signal distortions and hence a degradation OSNR = 3.85 − 10.73λ + 2.13λ2 + 9.75λ3 , (10) in the BER of the received signal. The group delay between two polarisation components is called the differential group The radio frequency transmission response provide the delay, ∆τ. Its average is the Polarization mode dispersion relative loss or gain in a wireless communication system (PMD) delay in psec and is expressed by the PMD links with respect to the signal frequency. Any signal coefficient in ps/km1/2. The PMD does not increase linearly, attenuation due to the wireless communication links can be but with the square root of transmission distance. expressed as follows [12]: ⎛ P ⎞ Δτ = L .Δτ coeff , (16) Transmission dB = 10log⎜ transmitter ⎟ , (11) () ⎜ ⎟ where L is the transmission distance, and ∆τ is the PMD ⎝ Pincident ⎠ coeff coefficient. Taking into account the statistical character of where P is the radio frequency power calculated at the transmitter PMD variations, if a 1 dB power pentaly due to PMD can be output of the receiver, and P is the radio frequency incident accepted then: power calculated at the input to the laser transmitter. Based T on curve fitting Matlab Program, the fitting equations Δτ max ≤ , (17) between transmission response, operating radio frequency, 10 and amplification range are [12]: where T is the bit period. Setting T as 1/B0 we obtain: 1 L ≤ , (18) 2 3 2 2 Transmission ()dB = 10.82 − 2.05 f + 7.42 f − 4.23 f 100.B0 .Δτ coeff

(without amplification), (12) where B0 is the bit rate. The receiver sensitivity is defined as Transmission (dB) = 3.09 + 13.65 f − 2.56 f 2 + 1.85 f 3 the minimum number of photons per bit necessary to -9 (with amplification) (13) guarantee that the bit error rate (BER) is smaller than 10 . The Shannon capacity theorem to calculate the maximum This sensitivity corresponds to an optical energy hν n0 and data transmission bit rate or the maximum channel capacity an optical received power as follows: for the wireless optical links is as follows: Preceiver = hυ n0 B0 , (19) C = B.W log 1 + OSNR , bits / sec (14) 2 () This power is proportional to the total bit rate B0. In a saturated attenuation-limited link, the link budget in dBm III. 2. Digital wire optical cable link design units as follows [14, 15]:

Digital communications systems have many advantages Preceiver = Ps − Pc − Pm −α L, dB / km (20) over analogue systems brought about by the need to detect where Ps is the source power, Pm is the modulator power, α only the presence or absence of a pulse rather than measure is the fiber loss in dB/Km, P is the coupling loss, and L is the absolute pulse shape. Such a decision can be made with c the fiber length. When Preceiver is converted to dB, it is reasonable accuracy even if the pulses are distorted and evident that P increases logarithmically with the data noisy. For single wavelength systems, repeaters allow new receiver rate B0. Therefore as the bit rate increases the power clean pulses to be generated if required, preventing the required to maintain the desired BER also increases. With accumulation of distortion and noise along the path. this in mind, the derived maximum length of the digital Chromatic dispersion is caused by a variation in group optical link [15]: velocity in a fibre with changes in optical frequency. The set of pulses generated by a laser which by virtue of the laser 1 ⎛ n0 hν B0 ⎞ L = ⎜ Ps − Pc − Pm − 10log ⎟ , Km (21) linewidth and signal modulation contains a spectrum of α ⎝ 10−3 ⎠ (IJCSIS) International Journal of Computer Science and Information Security, Vol. 3, No. 1, 2009

200 30

0.85 µm 1.55 µm 180 1.3 µm 1.53 µm 1.5 µm 1.55 µm 25 160

140 20

120

100 15

80

10 60 Signal attenuation, dB/ Km Km dB/ Signal attenuation, Optical signal to noise ratio, OSNR, OSNR, dB ratio, to noise Optical signal 40 5

20

0 0 0.211.82.63.44.25 0.20.71.21.7 Visibility, Km Wireless optical link distance, L, Km

Figure 5. Variations of the signal attenuation with visibility for Figure 7. Variations of optical signal to noise ratio with wireless different laser diode wavelengths at the assumed set of parameters. optical link distance at the assumed set of parameters.

0 7 wireless link without amplification -2 6 wireless link with amplification

-4

5 -6

-8 4

-10

3 -12 Ray losses, dB Signal transmission, dB dB Signal transmission, -14 2

-16 Lens diameter = 50 mm 1 Lens diameter = 100 mm -18 Lens diameter = 150 mm

-20 0 100 150 200 250 300 350 400 450 500 50 135 220 305 390 475 560 645 730 815 900

Beam diameter at receiver, mm Transmitted radio frequency, MHz

Figure 6. Variations of the ray losses with beam diameter at receiver Figure 8. Variations of wireless transmission with transmitted radio for different lens diameter at the assumed set of parameters. frequency at the assumed set of parameters.

(IJCSIS) International Journal of Computer Science and Information Security, Vol. 3, No. 1, 2009

100 600 wireless link distance= 0.4 Km 90 wireless link distance= 0.18 Km wireless link diatance= 0.02 Km 500 80

70 Without amplification 400 60

50 300 1.55 µm 1.3 µm 40 0.85 µm 200 Transmission distance, Km Km Transmission distance, 30 Mbit/sec rate, Transmission data 20 100

10

0 0 50 135 220 305 390 475 560 645 730 815 900 0 500 1000 1500 2000 2500 3000

Transmitted radio frequency, MHz Transmission data rate, Mbit/sec

Figure 9. Variations of transmission data rate with transmitted radio Figure 11. Variations of the transmission distance for digital optical frequency at the assumed set of parameters. link with transmission data rate at the assumed set of parameters.

10 20 wireless link distance = 5 Km 9 wireless link distance = 3 Km wireless link distance = 0.6 Km 8 16

7 With amplification Attenuation limit with LD/APD 6 12 Attenuation limit with LED/PIN

5

4 8 Transmission distance, Km Km Transmission distance, 3 Multi-mode fiber Gbit/sec rate, data Transmission 2 4

1

0 0 50 135 220 305 390 475 560 645 730 815 900 0 100 200 300 400 500

Transmitted radio frequency, MHz Transmission data rate, Mbit/sec

Figure 10. Variations of transmission data rate with transmitted radio Figure 12. Variations of the transmission distance for digital optical frequency at the assumed set of parameters. link with transmission data rate at the assumed set of parameters.

(IJCSIS) International Journal of Computer Science and Information Security, Vol. 3, No. 1, 2009

160 The total rise time depends on: transmitter rise time (ttx), group velocity dispersion (tGVD), modal dispersion rise time (tmod), and receiver rise time (trx), therefore the total rise 140 Single-mode fiber time, tsys, for the system is [15]: 1 n 2 ⎡ 2 ⎤ 120 tsys = ⎢∑ti ⎥ (22) ⎣i=1 ⎦ Total rise time of a digital optical link should not exceed 100 70% for a non return to zero code (NRZ) bit period, and 35% of a return to zero (RZ) code bit period. Assuming both transmitter and receiver as first order low pass filters, the 80 transmitter and receiver rise times are given by: 350 350 60 ttx = trx = = , nsec (23) Btx Brx Transmission distance, Km Km Transmission distance, where Btx and Btx are the transmitter and receiver 40 bandwidths in MHz. The bandwidth BM (L) due to modal Attenuation limit with LD/APD dispersion of a digital optical link length L is empirically Attenuation limit with LED/PIN given by: 20 B0 BM (L) = , (24) Lq 0 where B0 is the bandwidth per Km (MHz-Km product) and 0 750 1500 2250 3000 3750 4500 0.5 < q < 1 is the modal equilibrium factor. Then the modal Transmission data rate, Mbit/sec dispersion rise time is given by:

q Figure 13. Variations of the transmission distance for digital optical 0.44 440 L link with transmission data rate at the assumed set of parameters. tmod = = , nsec (25) BM B0

tGVD = D Lσ , nsec (26) λ where D is the chromatic dispersion parameter

(nsec/nm.km), σλ is the half power spectral width of the source (nm), and L is the optical link distance in Km. 200 Therefore the total rise time system is given by [15]:

NRZ dispersion limit 1 2 2 2 2 2 2 2q 2 2 RZ dispersion limit tsys = [ttx + trx + D σ λ L + ()440 L / B0 ] , nsec (27)

160 IV. RESULTS AND DISCUSSIONS Single-mode fiber IV. 1. Wireless optical link

120 The main objective of the wireless optical link design is to get as much light as possible from one end to the other, in order to light as possible from one end to the other, in order to receive a stronger signal that would result in higher link

80 receive a stronger signal that would result in higher link margin and greater link availability. As shown in Table 1,

Transmission distance, Km Km distance, Transmission the proposed wireless optical link parameters to achieve maximum both tranmission link distance and transmission

40 data rate. TABLE 1. PROPOSED WIRELESS OPTICAL LINK DESIGN PARAMETERS.

Power transmitted (PT) 100 mWatt 0 Operating wavelength range (λ) 0.85 µm to 1. 55 µm 0 750 1500 2250 3000 3750 4500 Transmitter beam diveregnce (θ) 115 degree Transmission data rate, Mbit/sec Recriver diameter (DR) 0.1-0.5 m Link distance range 0.1 to 10 Km Figure 14. Variations of the transmission distance for digital optical Receiver sensitivity (SR) or power 2 µWatt link with transmission data rate at the assumed set of parameters. received Transmitter and receiver losses (η) 50 % (IJCSIS) International Journal of Computer Science and Information Security, Vol. 3, No. 1, 2009

Based on the assumed set of the controlling parameters for Also in the same way, based on the assumed set of the wireless optical link design to achieve the best transmission controlling parameters for wire optical cable link design to bit rates and transmission distances and the set of the figures achieve the best transmission bit rates and transmission from (5-10), the following facts are assured: distances and the set of the figures from (11-14), the 1) Fig. 5 has indicated that as the transmission distance following facts are assured: (visibility) increases, the signal attenuation decreases at the same optical signal wavelength. While as the optical 6) As shown in Fig. 11, as the transmission data rate signal wavelength increases, signal attenuation decreases increases, the transmission distance decreases at the same at the same transmission distance. optical signal wavelength. Moreover as the optical signal wavelength increases, the transmission distance also 2) As shown in Fig. 6, as the beam diameter at receiver increases at the same transmission data rate. increases, the ray losses also increases at the same lens diameter. While as the lens diameter increases, the ray 7) Figs. (12, 13) have demonstrated that as the transmission losses decrease at the same beam diameter at receiver. data rate increases, the transmission distance decreases at 3) Fig. 7 has demonstrated that as wireless optical link the same attenuation limit for both LD/APD and LED/PIN distance increases, the optical signal to noise ratio (OSNR) for both single and multi-mode fibers. While as the decreases at the same optical signal wavelength. attenuation limit with both LD/APD and LED/PIN Moreover, as the optical signal wavelength increases, the decreases, the transmission distanceincreases at the same OSNR also increases at the same wireless optical link transmission data rate. distance. 8) Fig. 14 has assured that as the transmission data rate 4) As shown in Fig. 8, as the transmitted radio frequency increases, the transmission distance decreases at the same increases, the signal transmission also increases for both dispersion limit for both return to zero (RZ) and non amplification and non amplification techniques. But with return to zero (NRZ) codes. Moreover as the dispersion amplification technique offered high signal transmission. limit for both RZ, and NRZ decrease, the transmission

5) Figs. (9, 10) have indicated that as the transmitted radio distance increases at the same transmission data rate for frequency increases, the transmission data rate also single mode fiber link. increasesin both cases of amplification and non amplification techniques at the same wireless link distance. While, as the wireless link distance increases, the V. CONCLUSIONS transmission data rate decreases at the same transmitted radio frequency. Moreover with amplification techniques In a summary, we have investigated and analyzed the offered both high transmission link diatance and transmission performance characteristics for both digital transmission data rate. wire and wireless optical links in local and wide areas optical networks. We have demonstrated that the larger of IV. 2. Wire optical cable link the optical signal wavelength, the higher transmission The main goal is how to develop a simple point to point distance for both wireless and wire digital optical links. digital wire optical cable link design, taking into account Moreover, we have demonstrated that with amplification link power budget calculations and link rise time techniques, which added additional costs for wireless calculations. A link should satisfy both these budgets such as system, the wireless optical link offered both high transmission distances, and data rate for a given BER. The transmission distances and transmission data rate. In the data transmission bit rate, and transmission distances are the normal case (without amplification), the digital wire major factors of our interest for designing digital wire optical cable link offered both high transmission distances optical cable link. Table 2 shows the proposed wire digital and data rates over wireless optical link with optical cable link parameters to calculate both transmission amplification. Also, we have assured that the use of distances and date rates. LD/APD couplers offered maximum transmission distances and data rates over the use of LED/PIN couplers. TABLE 2. PROPOSED DIGITAL WIRE OPTICAL Therefore it is evident that the digital wire optical cable CABLE LINK DESIGN PARAMETERS. links offered the best performance in cost, transmission distances, and transmission data rates over wireless optical Power transmitted (P ) 100 mWatt T links. Power received (Preceiver) 2 µWatt Fiber Loss 3.5 dB/Km Couplers [LED-PIN] 1.5 dB Bandwidth per Km (B0) 900 MHz-Km Modal equilibrium factor (q) 0.7 50 nm LED [σλ] LD [σλ] 1 nm Couplers [LD-APD] 8 dB Material dispersion (Dmat) 0.07 nsec/nm.Km (IJCSIS) International Journal of Computer Science and Information Security, Vol. 3, No. 1, 2009

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